The present invention relates to a mechanism for preheating a source metal for a melt and, more particularly, to a preheating mechanism having a combination of independent combustion and preheating devices and suitable for heating and melting of nonferrous metals such as aluminum and zinc.
Most recent nonferrous metal melting furnaces use a combusted exhaust gas to preheat a melt source for the purpose of energy saving. In a conventional melting furnace of this type, a heat exchanger is used to heat primary or secondary combustion air by a high-temperature combusted exhaust gas, thereby decreasing the fuel expense. However, in a typical example of the conventional nonferrous metal melting furnace, a leading portion of a gas flue of the melting furnace is utilized as a source charging/prehating portion. For example, in melting of aluminum scraps and die cast recycle materials, most of the melting furnaces with a preheating chamber used as source preheating type melting furnaces or fast melting furnaces are exemplified by a melting furnace shown in FIG. 1.
Referring to FIG. 1, a preheating tower 2 made of the same refractory wall as the melting furnace extends upward from the peripheral portion of the upper surface of a reverberatory furnace 1. The preheating tower 2 also serves as a gas flue and has an exhaust port 3 at its upper portion. A source for a melt such as scraps is charged from a charging port 4 at the top and drops downward through the preheating tower 2 by its own weight. The scraps are heated by the exhaust gas rising from the lower side. The source is melted by a high-temperature combustion gas from a melting burner 6 at a chute-like melting portion 5 having a lower inclined portion below the preheating tower 2. The melt in the furnace is heated by a heating burner 6'. In the melting furnace with this structure, the temperature of the exhaust gas is excessively high, and the gas path in the preheating tower is eccentric. Only the source along the gas path tends to be locally overheated and melted, and most of the exhaust gas is exhausted without being used to heat the source. As a result, the effective heat conduction area of the charged source is decreased, and heat utilization is degraded. Furthermore, a high-temperature molten metal in the preheating stage increases an excessive oxidation loss of the metal and an evaporation loss. As a result, the yield of melt is decreased.